Biologically, cholesterol is eliminated from the body by conversion to bile acids and excretion as neutral steroids. Bile acids are synthesized from cholesterol in the liver and enter the bile as glycine and taurine conjugates. They are released in salt form with bile during digestion and act as detergents to solubilize and consequently aid in digestion of dietary fats. Following digestion, bile acid salts are mostly reabsorbed in the ileum, complexed with proteins and returned to the liver through hepatic portal veins. The small amount of bile acid salts which is not reabsorbed by active transport is excreted via the distal ileum and large intestine, which represents a major route for the elimination of cholesterol from the body.
Therefore, reabsorption of bile acids, which can be present as the corresponding salts or conjugates, from the intestine conserves lipoprotein cholesterol in the bloodstream. As such, reducing reabsorption of bile acids within the intestinal tract can lower levels of bile acid circulating in the enterohepatic system, thereby promoting replacement of bile acids through synthesis from cholesterol in the liver. The result is a lowering of circulating blood cholesterol levels.
One method of reducing the amount of bile acids that is reabsorbed is oral administration of compounds that sequester the bile acids within the intestinal tract and cannot themselves be absorbed. The sequestered bile acids consequently are excreted.